I have the black circle with the arrow, on the App Center icon is shows the red star,when I click on it it shows Twitter with the red star, but it also says Twitter not installed (I never used it). What do I need to do here?
When in app world go to my world and then while holding the alt key press R then S and then T. It will reset your app world and hopefully the problem app will disappear. Hopefully that will work for you.
I don't use Twitter and I have the same notification. It's just letting you know that there is an updated version of Twitter available. I'm just ignoring it.